JP5000565B2 - Pellet for manufacturing transparent parts and manufacturing method and manufacturing apparatus thereof - Google Patents

Description

  The present invention relates to a transparent part manufacturing pellet used for forming an optical part such as a transparent cover or a lens that covers a display unit, or other transparent parts with a synthetic resin, a manufacturing method thereof, and a manufacturing apparatus.

  A transparent cover that covers a display panel such as a liquid crystal panel is provided in the display unit of the portable device. This transparent cover is formed of a transparent resin material. However, in order to make the display image of the display panel clearly visible, it is necessary that no foreign matter is mixed in the transparent cover. The same applies to lenses, prisms, and other optical components formed of a transparent resin material.

  In the step of forming the transparent parts such as the transparent cover and the optical parts with a synthetic resin, standardized resin pellets are used so as to have a certain shape and size. In the transparent part manufacturing process, the resin pellets are supplied to a melt extruder, and the resin pellets are heated and pressurized and kneaded in the melt extruder to be in a molten state, and the molten resin is extruded from the die. The extruded molten resin is injected into a mold having a cavity in the shape of the part to be molded, thereby forming a transparent part.

  However, a fine foreign substance may be mixed in the transparent part molded in the conventional manufacturing process. If foreign matter is mixed inside, when used as a transparent cover, the foreign matter is displayed in a dirty state in the image of the display panel below it. In the case of an optical component such as a lens or a prism, there is a possibility that the optical function may be hindered by the inclusion of the foreign matter.

  The frequency of foreign matter mixing in transparent parts depends on the environment of the manufacturing process, but in the research process leading to the present invention, one of the causes of foreign material mixing is the shape of the resin pellet and the manufacturing process of the resin pellet. I was able to confirm that it exists.

  As a method for producing resin pellets, the strand systems described in Patent Document 1 and Patent Document 2 below are known. In this strand system, the melted and extruded molten resin is extruded by a strand die and cooled as a strand (string). The cooled and cured strand is sent to a pelletizing process, where the strand is held by a holding roll and cut to a specified length by a cutter roll.

  In order to melt the resin pellets uniformly in the process of manufacturing the transparent part, it is important to align the shape and dimensions of the resin pellets uniformly according to the standard. By supplying resin pellets having a uniform shape and size to a melt extruder, it is possible to uniformly melt individual resin pellets. Therefore, in the pelletizing step, it is necessary to firmly hold the strands that are continuously fed out with a holding roll and cut individual resin pellets with a cutter roll.

However, in the conventional pelletizing process, when the strand is held by the holding roll or when the strand leaves the holding roll, a small piece of resin is peeled off from the strand or the resin pellet after cutting, and this small piece is applied to the surface of the resin pellet. It has been confirmed that it adheres or mixes in the resin pellet group. In this case, in the manufacturing process of the transparent part, it is unavoidable that the small pieces are mixed together with the resin pellets in the melt extruder. In the melt extruder, even if an attempt is made to melt the resin pellets uniformly by sufficiently applying heat and pressure to the resin pellets of uniform shape and size, the small pieces sufficiently smaller than the resin pellets are present. , Not enough heat and pressure on this piece. For this reason, the small piece is pushed out while being mixed in the transparent resin without being sufficiently melted, and the small piece tends to remain as a foreign substance in the molded transparent part.
JP-A-6-218728 JP 2000-242971 A

  The present invention solves the above-described conventional problems, and the outer shape can be formed with high precision to a prescribed shape and size, and the small pieces are prevented from falling off from the surface. It is an object of the present invention to provide a transparent part manufacturing pellet, a manufacturing method thereof, and a manufacturing apparatus which are difficult to mix.

In the transparent resin pellet used as a supply source of the molten resin in the step of producing a transparent part by curing the molten resin,
An indentation that is pressed when cutting into a predetermined shape and a predetermined dimension is formed on the outer surface, and the indentation is gradually spaced from the inner bottom surface of the flat surface to the outer surface from the inner bottom surface It has a sloping inner surface that widens.

  In the pelletizing process, the resin pellet of the present invention is cut in a state of being firmly held so that the indentation is formed on the outer surface thereof, so that the outer shape and dimensions of the resin pellet are uniformly aligned. In the melt extrusion machine in the manufacturing process of transparent parts, it is uniformly pressurized and easily heated. Further, since the indentation has a shape having an inner bottom surface of a flat surface and an inclined inner side surface in which a facing interval gradually increases from the inner bottom surface toward the outer surface, the resin from the outer surface of the resin pellet in the pelletizing step This makes it difficult to remove small pieces. Therefore, when manufacturing a transparent part with a resin pellet, it can prevent that the resin small piece which cannot fully fuse | melt inside the transparent part remains.

The method for producing resin pellets of the present invention includes a step of melting and extruding a transparent resin material to form a strand,
Cooling the strand;
While holding the strand with a holding roll, and having a pelletizing step of cutting to a predetermined length with a cutter roll,
In the pelletizing step, the inner surface of the strand is inclined to the outer surface of the flat surface and the inclined inner surface is gradually widened from the inner bottom surface toward the outer surface by the convex portions provided on the surface of the holding roll. The strand is cut with the cutter roll while forming an indentation having the following.

  In the resin pellet of the present invention and the method for producing the resin pellet of the present invention, a cyclic olefin is preferably used as the resin forming the resin pellet.

In addition, the resin pellet manufacturing apparatus of the present invention includes a melt-extruded portion that melts and extrudes a transparent resin material to form a strand,
A cooling section for cooling the strand;
While holding the strand with a holding roll, and having a pelletizing part that cuts to a predetermined length with a cutter roll,
A plurality of convex portions for holding the strands are provided on the outer peripheral surface of the holding roll, and the convex portions have a truncated pyramid shape or a truncated cone shape.

  As described above, when the convex shape of the truncated cone or truncated cone shape of the holding roll is formed, it can be cut into individual resin pellets while the strand is securely held by the holding roll. The shape and dimensions of the subsequent resin pellets can be made uniform. Further, when the convex portion is separated from the strand, it becomes difficult to damage the resin on the surface of the strand, and it is possible to prevent a small piece of resin from being mixed when forming the resin pellet.

  The present invention can reduce the probability of occurrence of a phenomenon in which a small piece of resin that is not sufficiently melted remains inside the transparent part as a foreign object when forming the transparent part, thereby improving the quality of the transparent part. it can.

  FIG. 1 is an explanatory view of a production apparatus for producing resin pellets of the present invention, and FIG. 2 is an enlarged view showing a pelletizing section of the production apparatus. FIG. 3 is a perspective view of a resin pellet produced by the production apparatus, and FIG. 4 is an enlarged perspective view showing an indentation formed on the outer surface of the resin pellet. FIG. 5 is an enlarged perspective view showing the shape of a convex portion formed on the surface of the holding roll shown in FIG. FIG. 6 is an enlarged perspective view of a protrusion provided on the holding roll of the second embodiment. 7 and 8 are perspective views showing examples of transparent parts manufactured from resin pellets.

  A resin pellet manufacturing apparatus 1 shown in FIG. 1 includes a melt-extrusion unit 2, a cooling unit 3, and a pelletizing unit 4.

  The melt extrusion unit 2 is provided with a melt extruder 10. The melt extruder 10 is provided with a screw shaft 11 therein. The melt extruder 10 is a multi-screw extruder having a plurality of screw shafts 11 provided therein. A strand die 12 is provided at the discharge portion of the melt extruder 10. The strand die 12 is provided with a plurality of nozzles 12 a corresponding to the number of screw shafts 11.

  Although a feeder and a mixer for measuring and mixing the resin material are provided in the front stage of the melt extruder 10, these are not shown in FIG.

  The synthetic resin material supplied to the melt-extrusion unit 2 is a transparent resin for manufacturing a transparent cover that covers a display unit such as a portable device or an optical component such as a lens or a prism. The transparent resin is a thermoplastic resin, and for example, a cyclic olefin copolymer (COC) is used. Cyclic olefin copolymer has excellent optical properties such as light transmittance of 90% or more, low birefringence, and excellent mechanical properties such as rigidity and strength.

  The resin material weighed and mixed by the feeder or mixer is heated and pressurized by the melt extruder 10 to be kneaded to become a molten resin, and is continuously extruded as a strand 30 having a predetermined diameter by the strand die 12. The strand 30 has a circular, oval, or elliptical cross section, and the cross-sectional shape is uniform in each part of the length method.

  In the cooling unit 3, cooling water 16 is stored in the cooling tank 15, and cooling guide rolls 17 and 17 are provided in the cooling tank 15. The strand 30 pushed out by the strand die 12 is cooled by being guided in the cooling water 16 by the cooling guide rolls 17 and 17. The cooled strand 30 is taken out from the cooling tank 15 by the take-out roll 18, guided by the guide rolls 19 a and 19 b, and sent to the pelletizing unit 4.

  The pelletizing unit 4 is provided with a pair of holding rolls 21a and 21b. The cooled strand 30 is cut into a length dimension defined by the rotating cutter roll 22 while being continuously fed by the holding rolls 21a and 21b or intermittently fed, thereby forming a resin pellet 31. Is done. Individually cut resin pellets 31 are collected in a collection box 23.

  FIG. 2 shows an enlarged structure of the pelletizing unit 4. As shown in FIG. 2, a plurality of convex portions 25 are formed on the respective surfaces of the holding rolls 21a and 21b. The holding rolls 21a and 21b face each other at regular intervals and are driven to rotate in opposite directions. The cooled strand 30 is held by the holding roll 21a and the holding roll 21b and sent out.

  The cutter roll 22 is provided with blades 22a arranged on the surface thereof at a constant pitch in the circumferential direction. A receiving die 24 is provided at the lower part of the cutter roll 22, and the strand 30 sent out by the holding rolls 21 a and 21 b is received from below by the receiving die 24 and is continuously rotated by the blade 22 a of the cutter roll 22. Disconnected.

  Since the strand 30 is firmly held by the holding roll 21a and the holding roll 21b having the convex portions 25 on the surface and sent out and cut by the cutter roll 22, the resin pellet 31 after being cut has a uniform length. It is formed in the size. As shown in FIG. 3, the cut resin pellet 31 has an outer peripheral surface 31a that is a cylindrical surface or an elliptical cylindrical surface, and both end surfaces 31b and 31b that are perpendicular to the central axis OO of the cylindrical surface. It becomes a surface.

  When the resin product is shaped by the resin pellets 31, a large number of the resin pellets 31 are supplied to the melt extruder. By uniformizing the shape and dimensions of the resin pellets 31, the resin pellets 31 are heated uniformly. And can be melted by applying pressure. Further, as shown in FIG. 3, the strand 30 is firmly held by the holding roll 21 a and the holding roll 21 b and sent out, so that the protrusion 32 is pressed against the outer peripheral surface 31 a of the resin pellet 31. Is formed.

  FIG. 4 shows the shape of each indentation 32 formed on the outer peripheral surface 31a of the resin pellet 31, and FIG. 5 shows the convex portions 25 formed on the surfaces of the holding roll 21a and the holding roll 21b.

  The convex portion 25 has a top portion 25a which is a flat surface and four inclined side surfaces 25b each of which is a flat surface, and the shape thereof is a so-called truncated quadrangular pyramid. The top part 25a is a flat surface of a rectangle or square, or a flat surface of a rhombus or a parallelogram, and the top part 25a is parallel to a plane in contact with the outer peripheral surfaces of the holding rolls 21a and 21b. Further, the shape of the skirt portion of the convex portion 25 is the same as that of the top portion 25a, and is a rectangle, a square, a rhombus, a parallelogram, or the like. The four inclined side surfaces 25b are tapered planes in which the facing interval gradually increases from the top portion 25a toward the outer peripheral surface of the holding roll.

  As shown in FIG. 4, the indentation 32 formed by the convex portion 25 has an inner bottom surface 32a at a position recessed from the outer peripheral surface 31a of the resin pellet 31, and extends from the inner bottom surface 32a toward the outer peripheral surface 31a. And two inclined inner side surfaces 32b. The inner bottom surface 32 a is a flat surface of a rectangle, square, rhombus, or parallelogram onto which the top portion 25 a of the convex portion 25 is transferred, and the inner bottom surface 32 a is parallel to the surface that the outer peripheral surface 31 a of the resin pellet 31 contacts. is there. Each inclined inner side surface 32b of the indentation 32 is a surface onto which the inclined side surface 25b of the convex portion 25 is transferred, and is a plane in which the facing interval gradually increases from the inner bottom surface 32a to the outer peripheral surface 31a.

  In the opening of the indentation 32, when the length of the diagonal on the long side is W1 and the length of the diagonal on the short side is W2, the long diagonal as shown in FIG. Directed parallel to -O, a short diagonal is directed to the side perpendicular to the central axis OO. The diagonal lengths W1 and W2 are both 1 mm or less. The depth D of the indentation 32 is preferably 2/3 or less of the long diagonal length W1, and more preferably 1/2 or less. The diagonal length Wa of the inner bottom surface 32a is preferably 2/3 or less of the length W1, and more preferably 1/2 or less. Similarly, the length Wb of the other diagonal line of the inner bottom surface 32a is preferably 2/3 or less, more preferably 1/2 or less of the length W2.

  The indentation 32 formed on the surface of the resin pellet 31 has a shape transferred by the convex portion 25 of the truncated quadrangular pyramid shown in FIG. 5, the inner bottom surface 32a is a flat surface, and the inclined inner side surface 32b is a relatively loose inclined surface. And the depth D is 2/3 or less of the long side. Therefore, variation in the shape of the indentation 32 transferred from the convex portion 25 can be reduced. Variations in the size and shape of the indentation 32 formed on the outer peripheral surface 31a of each resin pellet 31 can be reduced and the size and shape can be made uniform, so that the resin pellet 31 can be used as a melt extruder when manufacturing transparent parts. When supplied, heat and pressure can be applied uniformly to the individual resin pellets 31, and the resin pellets 31 can be uniformly melted.

  Further, in the step of forming the indentation 32 of the shape on the resin pellet 31, since the shallow indentation 32 is formed by the convex portion 25, the indentation 32 is applied when the convex portion 25 is pressed and when the convex portion 25 is separated from the indentation 32. In the manufacturing process of the resin pellets 31, it is possible to reduce the probability that small pieces of resin are dropped and mixed. Therefore, by mixing the resin small pieces with the resin pellets 31, it is possible to reduce such a phenomenon that the small pieces are not sufficiently melted and remain as foreign matters in the transparent part.

  In the transparent part manufacturing method, a plurality of resin pellets 31 are supplied to a melt extruder, and the resin pellets 31 are heated, pressurized, kneaded and melted by the melt extruder, and are attached to the melt extruder. Molten resin is extruded. And molten resin is inject | poured in a shaping | molding die, and a transparent component is manufactured. The transparent parts to be manufactured are the transparent cover 41 shown in FIG. 7 and the optical parts 42 such as the lens shown in FIG.

  Indentations formed on the outer peripheral surface 31a of the resin pellet 31 can be made uniform in shape and size of the individual resin pellets 31 by sending out and cutting the strands 30 held by the holding rolls 21a and 21b having the convex portions 25. 32 has a shallow and flat inner bottom surface 32a, and can be made into a uniform shape with little damage. Moreover, the reduction | decrease in which the small piece of resin and resin powder peel from the resin pellet 31 in the cutting process in the pelletizing part 4 can be reduced.

  Therefore, the resin pellets 31 can be uniformly melted by a melt extruder, and the probability that foreign matters, which are unmelted resin, are mixed in the molded transparent cover 41 and the optical component 42 or fogging can be reduced.

  The shape of the convex portions formed on the holding rolls 21a and 21b is not limited to a truncated quadrangular pyramid, as long as a flat top and an inclined side surface that gently slopes from the top to the base are formed. A truncated triangular pyramid or the like may be used. As shown in FIG. 6, a truncated cone convex portion 26 is used, and the shape of the convex portion 26 is transferred to form an indentation on the outer peripheral surface 31 a of the resin pellet 31. May be.

  Cyclic olefin / copolymer resin pellets 31 were produced by the strand system shown in FIGS. The cross section of the resin pellet was oval, the major axis was 2.7 mm and the minor axis was 2.1 mm. The length of the resin pellet was 3.0 to 3.1 mm. On average, 4 to 10 indentations 32 were formed on the outer peripheral surface of one resin pellet. The shape of the indentation 32 was about 0.65 mm for W1, about 0.5 mm for Wa, about 0.85 mm for W2, about 0.35 mm for Wb, and about 0.1 mm for depth D.

  The resin pellets were supplied to a melt extruder, and a rectangular transparent cover 41 shown in FIG. 7 was injection molded. The transparent cover was 60 mm × 70 mm and the thickness was 1.3 mm.

  As comparative examples, the resin pellets were cut from the strands using holding rolls 21a and 21b having the same W1 and W2 as those of the example and using convex portions of square pyramids with sharp tips. The diameter and length of the resin pellets and the number of indentations were the same as in the examples. However, although the indentation has an inverted quadrangular pyramid shape, there are many cases where damage is seen at the bottom. Using the resin pellets of this comparative example, a transparent transparent cover having the same dimensions as in the example was manufactured.

  This transparent cover is normal if it contains one foreign object with a maximum dimension of 0.15 mm or less, contains one or more foreign objects with a size exceeding 0.15 mm, or contains 0.15 mm or less. Even so, those containing two or more were considered defective.

  When 100,000 transparent covers of Examples and Comparative Examples were produced, the defective rate of the transparent cover using the resin pellets of the Example was 1.8%. The defective rate was 2.7%.

Explanatory drawing which shows embodiment of the manufacturing apparatus and manufacturing method of the resin pellet of this invention, FIG. 1 is an enlarged explanatory view of the pelletizing section shown in FIG. The perspective view which shows embodiment of the manufactured resin pellet, A perspective view of the indentation formed on the outer peripheral surface of the resin pellet, A perspective view of a convex portion formed on the surface of the holding roll, The perspective view which shows the other example of a convex part, The perspective view which shows the transparent cover of an example of a transparent component, The perspective view which shows the optical component of an example of a transparent component,

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pellet production apparatus 2 Melt extrusion part 3 Cooling part 4 Pelletizing part 10 Melt extruder 12 Strand die 15 Cooling tank 21a, 21b Holding roll 22 Cutter roll 25 Convex part 25a Top part 25b Inclined side surface 30 Strand 31 Resin pellet 32 Indentation 32a Inner bottom face 32b Inclined inner surface 41 Transparent cover 42 Optical component

Claims (5)

In the process of producing a transparent part by curing the molten resin, in the transparent resin pellets used as the supply source of the molten resin,
An indentation that is pressed when cutting into a predetermined shape and a predetermined dimension is formed on the outer surface, and the indentation is gradually spaced from the inner bottom surface of the flat surface to the outer surface from the inner bottom surface A resin pellet characterized by having an inclined inner side surface that expands.   The resin pellet according to claim 1, wherein the resin is a cyclic olefin. A step of melting and extruding a transparent resin material to form a strand;
Cooling the strand;
While holding the strand with a holding roll, and having a pelletizing step of cutting to a predetermined length with a cutter roll,
In the pelletizing step, the inner surface of the strand is inclined to the outer surface of the flat surface and the inclined inner surface is gradually widened from the inner bottom surface toward the outer surface by the convex portions provided on the surface of the holding roll. The strand is cut with the cutter roll while forming an indentation having a resin pellet manufacturing method.   The method for producing resin pellets according to claim 3, wherein the resin is a cyclic olefin. A melt-extruded portion for melting and extruding a transparent resin material to form a strand;
A cooling section for cooling the strand;
While holding the strand with a holding roll, and having a pelletizing part that cuts to a predetermined length with a cutter roll,
A plurality of convex portions for holding the strands are provided on the outer peripheral surface of the holding roll, and the convex portions have a truncated pyramid shape or a truncated cone shape. .

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